Focusing on a novel protein termed RGP1 that is uniquely expressed in germinal center B lymphocytes, we discovered a new family of proteins (RGPs) and isolated six of the family members. These proteins are expressed in multiple tissues and based on complementation studies in yeast they likely regulate G protein linked signal transduction pathways. We isolated genomic clones spanning murine RGP1, mapped the RGP1 genomic locus, and created a targeting construct for homologous recombination in ES cells. Our studies also identified a sub-family of protein kinases homologous to yeast STE20. The prototype, GC kinase, localizes to the germinal center (GC) region in lymphoid tissue and activates the stress activated protein kinase(SAPK) pathway, a MAPK related pathway. We identified another member of this subfamily and are testing whether it also activates the SAPK pathway. Studies of the transcription factor BSAP identified a naturally occurring splice product that behaves as a dominant negative, discovered that the context of a BSAP cis-element alters its functional activity, determined that CD40 stimulation increased while protein kinase C activation decreased BSAP levels, developed an intracellular FACS assay for BSAP to measure its levels in defined populations of cells, and isolated the BSAP gene and identified its promoter. Studies of B lineage specific promoters identified a crucial PU.1 site in the Bruton's tyrosine kinase promoter; identified critical elements in the CD19 and CD22 promoters; determined that the co- activator protein BOB-1 is critical for the induction of CD20 and early B cell development. Studies of the B cell membrane protein CD22 revealed that cross linking of CD22 activated a potent signal transduction pathway and that the recruitment of SH-PTP1C likely limits signal transduction through the pathway. Finally, we localized bcl-x, but not bcl-2, in those B cells undergoing selection in the germinal center implying a role for bcl-x in the rescue of germinal center B cells.